1. Field of the Invention
The present invention relates to a motion compensation device which compensates for motion causing image blur in an optical device, such as a camera, video camera, or binoculars, and, more particularly, the present invention relates to a motion compensation device having a motion detection signal correction unit to correct a motion detection signal according to a vibration state detected by a motion detection unit.
2. Description of the Related Art
A motion compensation device is known which compensates for motion of an optical system to suppress blur of an image formed by the optical system. The known motion compensation device detects motion causing image blur with an angular velocity sensor. A motion compensation optical system, which constitutes either a portion or all of a photographic optical system, is driven according to the detected motion in a direction to negate the motion causing image blur, thereby compensating for the motion causing blurring of the image. The motion of a camera which causes image blur has six (6) degrees of freedom: three (3) degrees of freedom of pitch, yaw and roll motion in the x, y and z axis directions; and three (3) degrees of freedom of translational motion. A known motion compensation device normally compensates for motion causing image blur with respect to motion having two (2) degrees of freedom consisting of pitch and yaw.
In a camera, there exist two main kinds of motion resulting in image blur which affect the camera. One type of motion is so-called hand shake, unintended by the photographer. A second type of motion is motion intended by the photographer, for example, a panning action or a composition change. In the case of a panning action intended by the photographer, when the camera following a subject begins its panning motion, a motion compensation device performs a motion compensation action at the commencement of panning motion because it cannot distinguish panning motion from hand shake. Because of the inability of the known motion compensation device to distinguish panning motion from hand shake, the phenomenon arises that an image in the camera viewfinder does not move, regardless of whether the camera vibrates horizontally.
Similarly, when the photographer initiates a composition change, the motion compensation device cannot distinguish between a composition change action and hand shake, and the motion compensation optical system is driven after the beginning of the composition change action. As a result, the image in the viewfinder does not move, regardless of whether the photographer moves the camera. Moreover, when the motion compensation optical system is driven as far as the movement range limit, motion compensation action becomes impossible, and movement of the image in the viewfinder does not occur until the stage at which the motion compensation optical system is driven to the movement range limit. The above-described phenomenon is highly sensitive to the photographer as the width of the motion compensation range widens, and a problem occurs in that it becomes difficult for the photographer to make intended changes on the viewfinder. On the other hand, when the motion compensation range is narrowed in order to avoid this phenomenon, a problem arises in that it is difficult to confirm the motion compensation effect in the viewfinder.
Moreover, because of size and cost aspects, the angular velocity sensor used for detecting motion is usually a vibration gyro type of angular velocity sensor. However, the structure of vibration gyro types of angular velocity sensors results in a very unstable output directly after a power supply is introduced. Moreover, because the frequency of hand shake is normally 1-15 Hz, a low pass filter of 1 Hz or below is used when calculating a central value (a value of .omega.=0 (zero)) of the output signal (angular velocity signal) .omega. of the angular velocity sensor. Because of this, the detection of the angular velocity signal .omega. is delayed corresponding to the frequency.
When photography is performed after the introduction of a power supply, the calculation of the value of .omega.=0 is not in time, and when the motion compensation device makes a correction, the drift of the angular velocity sensor is mistaken for a signal indicating motion causing image blur. As a result, even when photographing a stationary subject, it is possible that the photographic result is a photograph of a moving image as a result of the effect of the mistaken recognition of the drift of the angular velocity sensor.